Optical communication system using a circular electromechanical modulator



United States Patent 3,121,169 OPTICAL COMMUNICATION SYSTEM USING ACIRCULAR ELECTROMECHANICAL MOD- ULATOR Robert C. Benton, State College,Pa., assignor to Centre Circuits, Inc., State College, Pro, acorporation of Penns lvania y Filed Feb. 8, 1961, Ser. No. 87,860

20 Claims. (Cl. 250-199) This invention relates to a transducer formodulating a light beam, especially at high frequency. Both visiblelight and other light such as black light are contemplated, andparticularly light in the infrared portion of the hght spectrum.

More particularly, this transducer invention is embodied in aliquid-scaled, lens structure, the internal optics of which arecontrolled at desired frequencies up to 20 kc. and sometimes higher.Energy input causes a rapidly appearing and disappearing cloud of liquidcavitation bubbles to be generated and sonically brought into focus bythe transducer itself, so that these bubbles localize along the axis ofthe lens and cause the intensity of light transmitted to vary independence on the hydraulic power input. Such bubbles can be localizedwith fairly simple designs of the transducers, which are made ofmagnetostrictive material or piezoelectric material and which are shapedfor sonically focusing hydraulic energy either by themselves or elseprovided with a reflector therebehind such as a parabolic reflector tocreate the same effect.

With opaque or semi-opaque liquids, the instantaneous appearance thereinof a cloud of cavitation bubbles rcduces the light absorbingcharacteristics of the liquid to a point where a detectable light levelpasses from one side through and beyond the opposite side of the liquid.The instantaneous appearance of localized cavitation bubbles in atransparent liquid has the opposite effect; i.e., the normallyundiminished light is subjected to scattering and/or absorption becauseof the different indices of refraction as between the vapor bubbles andthe transparent liquid itself, and hence the level of the lighttransmitted is diminished.

The high frequencies achievable by my system are due to a combination ofhigh frequency phenomena. The transducer itself operates at known highelectrical frequencies and its size can be readily selected andproportioned for natural resonance at any of those frequencies. Theinstantaneous response of the transducer itself is, as a practicalmatter, matched by the instantaneous response of cavitation bubbleswhich result each time an electrical impulse is transduced mechanicallythrough a sonic medium into hydraulic cavitation energy. Finally, thefrequencies of the light beam modulated are high in the spectrum so thatthe use of a lamps beam is in no way a drawback from standpoint of speedand instantaneous response.

My invention is primarily adapted to use a light beam for establishingthe line of transmission to a photosensi tive surface which I providefor sensing the modulated light. Generically, however, any opticalradiation is contemplated, i.e., wave energy which can, for the instantpurpose, be controlled generally in accordance with the laws of optics.

Features, obiects and advantages of the invention will either bespecifically pointed out or become apparent when for a betterunderstanding thereof, reference is made to the following descriptiontaken in conjunction with the accompanying drawings in which:

FIGURE 1 is a block diagram of a system embodying the present invention;

FIGURE 2 is a longitudinal sectional view of a preferred embodiment ofthe transducer device;

FIGURE 3 is a schematic operational view taken transversely to show thetransducer action; and

FIGURES 4 and 5 are companion views correlating illustrative wave shapes(FIGURE 5) with the blocks appearing in FIGURES 1 and 4.

In FIGURE 1, the beam from an electric spot lamp 10 is focused so as tobe highly directive and has an axis establishing a line of transmission12. The beam falls on the photosensitive surface of a photocell device14, or other appropriate radiation detecting device, preferably locatedat a remote point which is reached by the light beam.

A light valve 16 interposed in the line of transmission comprises atransducer element 18:: immersed in the liquid within a transparentcontainer 20. The light valve 16 constitutes part of a lens systemincluding a posterior lens 22a, an anterior lens 24a, and one or morefilters 26 between the anterior lens 24 and the spot lamp 10; the filter26 preferably has a narrow pass band measured in terms of the spectrum,either visible or invisible.

Means for applying power to oscillate the immersed transducer element18a is provided as follows. An input power amplifier 28 couples anamplitude modulator 30 in the input of the transducer element 18a.Connected to modulator 30 is a modulating device 32 which modulatesinput to the transducer element 18a and which does so, for example, withcode signals, with voice signals, or with other suitable signals,preferably within the audio frequency range.

Also connected to the modulator 30 is an oscillator 34 having anadjustment 36 by which it can be adjusted to the frequency desired. Itis preferably adjusted to oscillate at a fixed electrical frequencyequal to the natural resonant frequency of the transducer element 18a,thus producing a maximum effect with relatively low input power.

If the modulating device 32 consists of a simple key, the input to thetransducer element 18a can be controlled by hand. If the modulatingdevice is a tape reader, the tape can be encoded in suitable code asdesired and transmitted fairly rapidly on the line of transmission 12.If the modulating device is a microphone, the input can be eithermodulated at voice frequencies or modulated otherwise within the AF andnear AF range or a combination of the two.

If the transducer element 18a is made of one of the magnetostrictivematerials having the not too uncommon property of exhibiting, say,negative elongation under weak flux followed by positive elongationunder stronger flux, it is desirable that a source of DC power 38 beconnected to the input of the transducer element so as to maintain apositive biasing flux through the core of the element at all times.Nickel has such magnetostrictive characteristics, in which case it isbiased with a fixed flux of appreciably higher density than required tomake the nickel take its minimal dimension (maximum negativeelongation). Changes in elongation will then be consistent,corresponding both in sense and magnitude with the flux produced by themodulated input to the transduccr element. In other words, increase inmodulated input causes increase of the elongation of this example oftransducer material and decrease of modulated input causes a lengthwisedecrease of the transducer material.

An electronic filter 40 couples the photocell device 14 to a combineddemodulator and output power amplifier unit 42 which reproduces the sameinput signal originating from the modulating device 32. The electronicfilter 40 is adjusted to pass only frequencies at or near the carrierfrequency of oscillator 34; hence, it prevents other flashing light orstray light from interfering with the transmission, at least when theinterfering light is in moderate quantities. The natural frequency forthe transducer element 18a is predetermined according to its mass, andshape and distribution of the material selected, so as to correspond tothe carrier frequency wanted. Accordingly, the power input required willbe of the order of a onethousandth of the power that might otherwise berequired to produce a like amplitude of vibration.

Following is an example of the specifications for the transducer elementof light valve 16:

Element 180 Cylindrical shape. Outside diameter 3 inches O.D.Cylindrical length 1% inches.

Radial thickness l6 inch.

Material Laminated nickel. Element 181: input 70-80 watts power If theoptical filter 26 is selected so as to have a pass band limited to theinfrared frequencies, the beam of light will be inconspicuous whichpasses through the lens system and beyond. It is preferred for thatreason.

In FIGURE 2, the principal components of the lens system of FIGURE 1 areidentified by new subscripts as elements 18b, 22b and 24b; in practice,they are combined so as to constitute a single transducer unit all inone. The transducer element 18b itself is actually a consolidation ofelements consisting of a laminated series of individual nickel rings 44,an electrical coil 46 toroidally wound thereabout. and an epoxyencapsulation 48 constituting a thin-walled plastic cylinder thereabout.The transducer element 18b fits within a generally cylindrical housingwith an annular clearance space 52 therebetween, said housing includinga clamping body 54 with a screwon clamping cap 56 and each presentingend flanges.

The lenses 22b and 24b are concentric to the line of transmission 12 andare etfective as walls to form transparent end plates of a container forthe sonic liquid 58. Each lens is clamped between one end of thetransducer element 18b and the confronting clamping flange of thehousing at that end.

An O-ring seal 60 carried in a groove in each interface of the lensesestablishes a liquid-tight joint at each end of the transducer element18b, at the same time enabling the element to vibrate radially withoutleakage. The clearance space 52 likewise accommodates radial expansionof the transducer but in practice, this clearance is slight inasmueh asthe total amplitude of vibration is adjusted so as to be barelyperceptible, if at all.

In assembly of the structure of FIGURE 2, the clamp ing body 54 of thehousing is placed in a vertical position resting on its end flange. Thelens 22b and the transducer element 18b are inserted, with theinterposed O-ring seal 60 disposed therebetween and resting in theannular groove in the lens 22b. The body of liquid 58 is then introducedto a point level with the upper edge of the unit 50 whereupon the lens24b and the interposed O-ring seal are placed in a covering positionthereover. After it is certain that all air bubbles have been excluded,the screw-on cap 56 is applied to complete the bipartite housing, thusclamping the seals 60 in fluid-tight relation.

In FIGURE 3, the laminated transducer element 18b under high frequencyflux stress from the coil 46 vibrates rapidly between its expanded andcontracted positions, the former having the dotted line position shownwith the diameter D, and the latter shown in the solid lines with thediameter D The resulting condensations and rarefaetions in the body ofliquid 58 travel at the speed of sound toward and away from thegeometric center of generation of the element 18b with the result thateach time the element assumes its expanded diameter B, there is aninstantaneously appearing core or column of cavitation bubbles 62 whichlocalizes about the line of transmission 12 (FIGURE 2); the diameter ofthis core of bubbles 62 is only some fractional part of the diameter Damounting in the general case to a cloud of approximately V4 of thatdiameter.

If a body of clear liquid 58 is used such as water, alcohol, or oil, alight beam following the line of transmission will be scattered and/orabsorbed each time the liquid is clouded by the instantaneous core ofcavitation bubbles, due for one reason to the fact that these cavitation(vapor) bubbles have a different index of refraction from the liquidphase. Hence the light level on the output side of the transducerelement 18b will diminish in correspondence with the concentration oflocalized bubbles.

:If the body of liquid 58 in the light valve is opaque so as to relyprimarily upon its absorptive properties, then I prefer a solution oflight-absorbing dye and alcohol or water, for example. The dye selectedshould have a different vapor pressure from the liquid in the mainsolution: in that way the cavitation bubbles will consist predominantlyof transparent vapor thus reducing the light absorbing properties of thesolution. When the amplitude of vibration of the element 18b is high, agood concentration of the localized cavitation bubbles can cooperativelytransmit a noticeable level of light to the output side of thetransducer. Certain inks can be employed as the proper liquid solutionso long as they are diluted sufficiently to be of a semi-opaque or nearsemi-opaque state.

Following each of the block elements of FIGURE 4 are examples A, B, C,D, E, F, G of FIGURE 5 illustrative of the respective modulated wave andlight intensity shapes for code transmission. Voice transmissions andother transmissions, particularly in the audio range, can be equallywell handled by the present device but for the sake of brevity, thesefurther examples of wave forms are not illustrated.

As herein disclosed, according to FIGURE 2, the magnetostrictivematerial of the body of the transducer element 18b is nickel. It isevident that a large group of magnetostrietive materials is availablefor these bodies including powder iron-nickel products, ferroeeramicproducts such as ferrox-eube" as it is commercially known by itsproprietary name, Alnifer, and various compositions of iron-nickelalloys. Each time the element vibrates, it physically disturbs theimmediate film of medium in contact with its circular interface, therebyfocusmg energy waves in the medium which travel at the speed of soundtowards the geometric center. The size and concentration of cavitationbubbles created at the focal point correspond to the amplitude of thevibration. The core of bubbles is approximately coextensive in lengthwith the transducer element along its axis.

also the drawing discloses that the O-ring seals 60 are recessed in agroove so as to protrude slightly into contact with a hat confrontingsurface on the transducer unit 50; this seal construction and contactenables the transducer unit 50 to float as it vibrates; self evidentlythere are other seal arrangements which can satisfactorily be employed,or no seals at all as schematically represented by the container 20 ofFIGURE 1 wherein the.

transducer element 18a is completely immersed within a container.

Variations within the spirit and scope of the invention described areequally comprehended by the foregoing description.

I claim:

l. In a device of the character described, a container with Oppositetransparent walls for holding liquid and adapted to have a light beamdirected on an axis through the walls of the container, and a transducerring of magnetostrictive material in said container and energizable withpulsating magnetostrictive power input for creating with respect to theoscillating circumference within the ring a cloud of instantaneouslyappearing and disappearing liquid cavitation bubbles in the geometriccenter of the ring in the area of said axis to vary the percentage oflight transmitted between said walls.

2. In a device of the character described, a container with oppositetransparent walls for holding liquid and adapted to have a light beamdirected normal to and through said walls, and a ring of transducermaterial in said container, and energizable with pulsating transducerpower whereby the entire circumference of the ring oscillates forcreating with respect to the circumference within the ring, liquidcavitation bubbles in the geometric center of the ring in the areabetween said walls to vary the intensity of light transmitted from onewall to the other, said walls constituting optical lenses.

3. In a device of the character described, a container with opposedtransparent walls for holding liquid, said container adapted to have alight beam directed therethrough between said walls, said wallsconstituting op tical lenses, a vibratile transducer ring in saidcontainer efiective when actuated with fluctuating energy for ereatinginstantaneously appearing and disappearing liquid cavitation bubbles tovary the intensity of light transmitted between said walls, said ringbeing encapsulated in a thin-walled plastic cylinder, and annular sealsdisposed one between each of the opposite ends of said cylinder and thewall at that end creating a liquid-tight joint whereby the cylinder iscapable of limited movement with the transducer ring without incurringleakage at the joint with the walls.

4. In a device effective to hold liquid for the purposes described, agenerally cylindrical housing and a generally cylindrical transducerelement arranged one within another and with an annular space between,and transparent plates disposed at opposite ends of the transducerelement and each clamped between an end of the transducer element andthe housing at that end for holding the liquid in said device in contactwith the transducer element, said transducer element having anelectrical coil wound thereon for receiving electrical impulses at thenatural frequency of said element and causing said element to vibrate atresonance. 7

5. In a device of the character described for holding fluid, a generallycylindrical housing and a generally cylindrical transducer elementarranged one within another with an annular space between, transparentplates disposed at opposite ends of the transducer element and eachclamped between an end of the transducer element and the housing at thatend, said transducer element having a toroidal coil wound thereon forreceiving electrical impulses at the natural frequency of saidtransducer element for causing the same to vibrate, and seals interposedbetween the transparent plate at each end of the transducer element andthe transducer element at that end for holding the fluid liquid-tightwithin the device.

6. In a system which transmits on a beam of light as the line oftransmission, a lens system in the line of transmission including aconfined liquid, a generally annular body of material selected from theclass consisting of piezoelectric and magnetostrictive materials, saidbody being immersed in said liquid in a disposition with its geometriccenter of generation at a point generally eoncentric with the areathrough which the beam passes, and energy applying means connected toapply energy to the body for imperceptibly changing the physicaldimensions of said body at high frequencies so as to physically disturbthe immediate film of liquid in'eontact therewith, thereby focusingenergy waves in the liquid at the geometric center of generation of saidbody for causing a cloud of cavitation bubbles to repetitively appearand disappear in line with the light beam.

7. In a system for transmitting on a beam of light as the line oftransmission, a lens system in the line of transmission including aconfined fluid sonic medium, a generally annular transducer body forconverting electrical energy to sonic energy and immersed in said mediumwith its geometric center of generation at a point concentric to thearea through which the light beam passes, and tuned electrical meansconnected to apply electrical energy to the transducer body forimperceptibly changing the physical dimensions of said transducer bodyat its natural resonant frequency so as to physically disturb theimmediate film of medium in contact therewith, thereby focusing energywaves in the medium which travel at the speed of sound to the geometriccenter of generation of said transducer body thereby causing aconcentrated cloud of cavitation bubbles to repetitively appear anddisappear in line with the light.

8. A lens system for controlling the transmission of light, comprisingmeans for restricting the amount of light in said system to a limitedpass band of frequencies and including a light filter. means forfocusing said light as a beam for effective directivity at a distanceand including lenses made of solid transparent material, means in whichthere is repetitively introduced a rapidly appearing and disappearingcloud to vary the quantity of light scattering away and/or absorbed fromsaid beam and including an incompressible transparent fluid, and sonicenergy emitting means for repetitively creating a group of temporarycavitation bubbles in said fluid so as to form the rapidly appearing anddisappearing cloud aforesaid, said sonic energy emitting meanscomprising transducer means in contact with said fluid and shaped toprovide a focusing point so as to concentrate said bubbles at a commonspot, said transducer means being geometrically arranged with respect tothe filter, lenses, and tluid so that the filter, lenses, and commonspot of bubbles are optically a-lined with the light in the system.

9. In a system of optical beam communication adapted to modulate a beamof optical radiations establishing a line of transmission through theatmosphere, an interposed fluid medium in the line of transmission,means to introduce from a ring of points sonic waves in said mediumcomprising high frequency transducer means in communication with thefluid of said medium in the ring of points aforesaid, said transducerbeing vibratable to introduce from the respective directions of saidpoints streams of waves in impingement against one another in the soleregion of confluence common thereto to create a concentratedcavitational disturbance therein and having an input, and power deliverymeans for applying power to vibrate said transducer comprising carriermeans to impress in the input of said transducer a fundamental carrierfrequency which at least approximates the natural resonant frequency ofthe transduceml 10. In a system of optical beam communication providedwith means for emitting a beam of optical radiations to establish theline of transmission, the combination comprising: interposed means inthe line of transmission having an electrical input and varying in itstransmitting property in response to said input; said interposed meansincluding a body of liquid; means to direct sonic waves in differentdirections into the body of said liquid comprising high frequencytransducer means having general, hollow cylindrical shape and beingwithin the cylindrical interior thereof in communication with the bodyof liquid; said transducer means being vibratable, in response to inputto the interposed means, to introduce from the locus of points definedby its cylindrical interior streams of waves in impingement against oneanother in the sole region of confluence common thereto thereby tocreate a locally concentrated cavitational disturbance therein; and amodulator device comprising modulating means and carrier means having afrequency higher than said modulating means, said carrier meansdeveloping a fundamental carrier frequency and being modulated by saidmodulating means; and means comprising a poweramplifier coupled betweenthe modulator device and said interposed means for impressing amodulated carrier signal in the input of said interposed means.

11. A lens system for controlling the transmission of light to a remotedemodulator type utilization apparatus 7 in photosensitive relationthereto, said system comprising means for restricting the amount oflight in said system to a limited pass band of frequencies and includinga light filter, means for focusing said light as a beam for effectivedirectivity at a distance and including lenses made of solid transparentmaterial, means in which there is repetitively introduced a rapidlyappearing and disappearing cloud to vary the quantity of lightscattering away and/or absorbed from said beam and including anincompressible transparent fluid, high frequency sonic energy emittingmeans for repetitively creating a group of temporary cavitation bubblesin said fluid so as to form the rapidly appearing and disappearing cloudaforesaid, said filter, lenses, fluid, and high frequency sonic energyemitting means being in optical alignment with the light, said highfrequency sonic enengy emitting means comprising transducer means incontact with the fluid and conforming to the arc of a circle andarranged in a location to provide a focusing region at the centerconcentrating said bubbles at a com mon region in the line of the light,said high frequency sonic energy emitting means operating in response toan input signal. I

12. For use with a system of optical beam communication utilizingoptical radiations for establishing a beam of transmission along a line:a beam valve comprising a beam-obstructing, fluid medium adapted to beinterposed in the line of transmission to modulate said optical beam;means to introduce from a ring of points sonic waves in said medium,including high frequency transducer means in communication with thefluid of said medium in the ring of points aforesaid; said transducermeans being vibratable to introduce from the respective directions ofall of said points streams of waves in impingement against one anotherin a common area of confluence thereby to create locally concentratedcavitational disturbances therein and having an input; and powerdelivery means for applying power to vibrate said transducer, includingcarrier means to impress in the input of said transducer a fundamentalcarrier frequency which at least approximates natural resonant frequencyof the transducer means.

13. For use with a system of optical beam communication provided withmeans for emitting a beam of optical radiations to establish the line oftransmission: the combination comprising means for interposition in theline of transmission having an electrical input and varying in itstransmitting property in response to said input, said interposed meansincluding a body of beam obstructing liquid; means to direct sonic wavesin different directions into the body of said beam obstructing liquid,including high frequency transducer means curved on the arc of a circle,and being in communication with the liquid along a circular locus ofpoints; said transducer means being vibratable, in response to input tothe interposed means, to introduce in the respective directionsaforesaid streams of waves from the circular locus of points inimpingement against one another in a common area of confluence therebyto create locally concentrated cavitational disturbances therein; and amod-ulator device comprising modulating means and carrier means having afrequency higher than said modulating means, said carrier meansdeveloping a fundamental carrier frequency and being modulated by saidmodulating means; and means including a power amplifier coupled betweenthe modulator device and said interposed means for impressing amodulated carrier signal in the input of said interposed means.

14. The method of utilizing a sonic medium to control the transmissionof light in a beam directed toward said medium, comprising the steps ofgenerating along a circular locus of points, repetitive waves of energyin said medium traveling at the speed of sound, and converginglydirecting said energy waves through the sonic medium so as to focus inthe precise region of the locus center at which cavitation bubblesrepetitively appear and disappear as a cloud due to the resultingcondensations and rarefactions of wave energy in the medium.

l5. Improved method useful in optically controlling a beam ofelectromagnetic radiations or the like following a line of transmission,including the steps comprising: generating from a circular locus ofpoints defined by transducer means, waves of energy of controlledmagnitude at electrical frequencies in a cavitatable medium havingvariable translucency; and projecting said waves from said circularlocus of points so that they impinge in the medium upon one anothercreating a highly localized cavitational disturbance at a region thereinwhich, when in optical coincidence in a 'line of radiation transmission,is effective to cause the radiation beam to be variably attenuated inpassing through the cavitatahle medium.

16. In a process useful in optically controlling a beam ofelectromagnetic communication radiations or the like following a line oftransmission: the improved steps comprising interposing a cavitatablefluid medium in alignment with the line of transmission; and contactingthe medium with the geometrically focused annular interior surface of avibrating transducer so as to project waves of energy of controlledmagnitude at the transducer frequency from the locus of points definedby said annular interior surface, into the medium for generating arepetitive cavitational disturbance which, when focused in a line oftransmission, causes a radiation beam passed through the medium to bevariably attenuated thereby as a function of the r titive cavitationaldisturbance.

17. In a method of utilizing a sonic medium to control the transmission,for communication purposes, of a beam of optical radiations directedtoward said medium: the improved steps comprising generating at a ringof points, repetitive waves of energy in said medium traveling at thespeed of sound; and projecting said waves of energy in a mutuallyconverging direction from each of the ring of points through the sonicmedium and at right angles to said beam of optical radiations so as tofocus said waves at a general region of concentration at whichcavitation bubbles repetitively appear and disappear as a cloud forscattering and/ or absorbing a portion of the optical radiations in saidbeam, said waves comprising a carrier component and a modulating signalcomponent.

18. A method of communicating by means of a line of transmission throughthe atmosphere to a remote receiving point, comprising the steps ofinterposing a fluid medium aligned with the line of transmission,introducing from a ring of points on a common oscillating body waves ofenergy into the medium which are of controlled magnitude at electricalfrequencies and which impinge on one another in a region at thegeometric center constituting the sole region of confluence and being inthe line of transmission, and projecting a beam of optical radiationsalong the line of transmission toward said remote receiving point andpassing through said medium whereby the cavitational disturbancescreated in said sole region of confluence modulate the intensity of thebeam as a function of the desired communication being transmitted.

19. A method of communication by means of a line of transmission throughthe atmosphere to a remote receiving point comprising the steps ofinterposing a fluid medium in alignment with the line of transmission,contacting the medium with the geometrically focused annular interiorsurface of a vibrating annulus of transducer material so as to introducefrom the common annulus waves of energy into the medium which are ofcontrolled magnitude at the vibrating frequency and which impinge on oneanother generating cavitational disturbances focused in a region at thegeometric center constituting the sole region of confluence and being inthe line of transmission, and projecting a beam 9 of optical radiationin the atmosphere in the direction of said remote receiving point andpassing in the line of transmission through said cavitationaldisturbances whereby the communication transmitted will be a function ofsaid disturbances.

20. The method of utilizing a sonic medium to control the transmissionof a beam of optical radiations directed toward said medium, said methodcomprising: generating along a circular locus of points, repetitivewaves of energy in said medium travelin'g at the speed of sound;directing said waves of energy in a converging direction through thesonic medium and at right angles to said beam of optical radiations soas to focus said waves in the precise region of the locus center andwith forced concentration by which cavitation bubbles repetitivelyappear and disappear as a cloud for scattering and/or absorbing aportion of the optical radiations in said beam, said waves comprising acarrier component and a modulating signal component; and sensing, by

by a demodulator, the remaining portion of optical radia- A tions insaid beam so as to reproduce said modulating signal component.

References Cited in the file of this patent UNITED STATES PATENTS1,894,942 Chromy Ian. 24, 1933 2,153,490 Wikkenhauser et a1. Apr. 4,1939 2,158,990 Okolicsanyi May 16, 1939 2,234,329 Wolff Mar. 11, 19412,287,587 Willard June 23, 1942 2,433,456 Jansen Dec. 30, 1947 2,449,166Hershberger Sept. 14, 1948 2,557,974 Kibler June 26, 1951 2,634,366Schimpf Apr. 7, 1953 2,707,749 Mueller May 3, 1955

1. IN A DEVICE OF THE CHARACTER DESCRIBED, A CONTAINER WITH OPPOSITE TRANSPARENT WALLS FOR HOLDING LIQUID AND ADAPTED TO HAVE A LIGHT BEAM DIRECTED ON AN AXIS THROUGH THE WALLS OF THE CONTAINER, AND A TRANSDUCER RING OF MAGNETOSTRICTIVE MATERIAL IN SAID CONTAINER AND ENERGIZABLE WITH PULSATING MAGNETOSTRICTIVE POWER INPUT FOR CREATING WITH RESPECT TO THE OSCILLATING CIRCUMFERENCE WITHIN THE RING A CLOUD OF INSTANTANEOUSLY APPEARING AND DISAPPEARING LIQUID CAVITATION BUBBLES IN THE GEOMETRIC CENTER OF THE RING IN THE AREA OF SAID AXIS TO VARY THE PERCENTAGE OF LIGHT TRANSMITTED BETWEEN SAID WALLS. 